[en] The foraging behaviour of ancient packrats is turning out to be a valuable source of data about the long-term environmental stability of proposed nuclear waste repositories. Material collected immediately round the pack rat's den and deposited in middens has been left in a perfectly preserved state due to mummification in an arid environment. The data from the middens yields very precise information about climate and ecological conditions at the time of their creation tens of thousands of years ago. (Author)